The present invention relates to mechanical heart valve prostheses. Mechanical heart valve prostheses generally operate hemodynamically, in conjunction with the pumping action of the heart, to take the place of a defective natural valve. These valves have generally been designed to function with one or more occluders each swiveling to open and close a passageway through a generally annular valve body within which the occluders are suspended.
Pyrolytic carbon has been determined to be adequately non thrombogenic for use as a heart valve material. The problem of combatting thrombosis in mechanical valves is presently felt to lie in preventing excess turbulence, high shear stresses and local regions of stasis. Blood is a very delicate substance, and even minor abuses caused by turbulence and high shear stress can cause either thrombosis or emboli generation at local regions of stagnation. Regions of the valve that are particularly susceptible to the formation of thrombosis are the areas where the leaflets are pivotably suspended.
U.S. Pat. No. 5,861,029 discloses a mechanical heart valve having two projections at each side of each leaflet, one projection of each pair of projections being located above a rim in the valve body passageway and the other one of each pair of projections being located below the rim, so that the rim between the projections of each pair holds the pivotable leaflets in the valve body passageway. Slots in the valve leaflets leave open passageways to the outside of the pivoting area of the leaflets when the leaflets are closed.
U.S. Pat. No. 5,354,330 discloses a mechanical heart valve with a valve body having an interior wall surface with knobs cooperating with recesses in the side edge of said leaflet for keeping the leaflets in position, also during pivoting between the closed and open positions.
A valve with particularly low propensity of causing thrombosis is disclosed in U.S. Pat. No. 5,641,324 (embodiments of this valve have been approved by the U.S. Food and Drug Administration for usage with particularly low dosages of anticoagulants in the aortic position). The valve has a pivot arrangement with two pairs of diametrically opposed pivot member sets each formed by an ear projecting laterally from the side edges of the leaflet and a cavity in the interior surface of its valve body, each ear projecting into one of the cavities. The ears are shaped to allow some regurgitant flow around the ears when the leaflets are closed.
U.S. Pat. No. 6,296,663 discloses a mechanical bi-leaflet valve in which the leaflets each have ears projecting into mutually opposite recesses in the annular body. In this valve, the leaflets have notches allowing some regurgitant flow along the ears when the leaflets are closed.
These mechanical valves are specifically designed for implantation in the left ventricle. Maximum pressure drops (pressure differences between locations immediately upstream and downstream of the valve or occluders thereof) over the closed cardiac valve in the right ventricle are typically about eight times smaller than over the closed cardiac valve in the left ventricle. Accordingly, when a mechanical heart valve prosthesis is implanted in the right ventricle the flow through the valve hinges when the valve leaflets are in the closed position is much smaller than when the same valve would have been implanted in the left ventricle. This lower flow through the valve hinges is a probable cause for a higher incidence of clots originating from the valve hinge areas in mechanical heart valve prostheses in the right ventricle than in mechanical heart valve prostheses in the left ventricle. For this reason, mechanical prosthetic heart valves have not been popular for implantation in the right ventricle. However, the generally less thrombogenic alternatives of allograft (homograft) and biological heart valve prostheses have a much shorter lifetime than mechanical heart valve prostheses. This disadvantage is often exacerbated when the heart valve prosthesis is applied as a right ventricle heart valve prosthesis, because many diseases resulting in a need of a right ventricular heart valve prosthesis are innate diseases, so that patients receiving a first right ventricular heart valve prosthesis, often have a life expectancy that is a multiple of the lifetime of an implanted allograft (homograft) or biological heart valve prosthesis and therefore can expect to require multiple heart valve replacements, each involving heart surgery or delivery via a catheter and each preceded by a period of relatively poor performance of the heart valve prosthesis approaching its end of lifetime.